Dia Ssf

I've been thinking about trading the DIA SSF with IB. I use Sierra Chart with IB data feed. The DIA SSF seems to have good volume to trade, but the only problem is, on IB the "last price" stays the same for about 30 minutes, and that's why I can't chart this. The bid and ask are continuously changing though. What's up with that???

Anyone here get clean SSF charts?

Also, anyone know if its possible in Sierra Chart to chart an SSF using the bid or ask price instead of last price?

I put the underlying stock on my trading page, and put the SSF below the stock. The bid/ask on the SSF follow the stock price.
The change in price of the stock is how much you're really up or down, not the last price the SSF traded at.

The bid/ask on the SSF are real, you can buy or sell at the prices quoted.